I would like to know under what circumstances, if any, contrails are
formed at low altitudes, like close to ground level. Can contrails be
formed by jets, commercial or fighter, if flying full speed at ground
level? Thanks.

Hello there

I will begin by saying that the temperature has to be lower than -40
degrees F at flight altitude to form a contrail, and it helps if the
humidity is high as well.

So, first of all, if you want to create a contrail at low altitude
(near ground level) you would have to be in a place where air
temperatures near the ground were -40 F or lower.    Now it may seem
that this would work in Antarctica in midwinter, but there is still
the humidity factor.  While Antarctica may be cold, most of it is also
desert with a very low humidity.

But, every once in a while, things are just right and contrails will
occur at ground level in the Antarctic 'desert,' sometimes causing a
visibility problem for jets that take too long to take-off.

Though this website is about "chemtrails," rather than contrails, the
information about ground level contrails in Antarctica is found about
a fourth of the way down the page.
http://www.chemtrailcentral.com/chemfaq.shtml - website is "Chemtrail
FAQs"

About a quarter of the way down this page you will find a photo of a
ground level contrail in Antarctica.
http://oldnewt.phys.unsw.edu.au/~pcalisse/Gallery/SouthPole/southpole.html
- If you click on the picture and enlarge it, you will find that it is
not even a jet but a prop driven aircraft. - "Pictures from the UNSW
AASTO 1999 and 2000 campaign"

In fact, the plane doesn't even have to be flying to form contrails,
just sitting around and doing nothing also does the trick. - - "The
sled will be of great value at the South Pole because of off-load
problems encountered early in the season. These problems stem from
contrails, which normally form when the aircraft is flying. Because of
the extreme cold temperatures at the Pole, the contrails form on the
ground when the aircraft is idling." - Quote from Antarctica Times - a
publication of the US Navy:
http://www.polar.org/antsun/oldissues96-97/astdec22.htm

Antarctica is not the only place where ground level contrails have
been observed. - - ". When the weather is as cold as it often is in
mid-winter in Alaska, Siberia and central Canada, contrails can even
form at ground level. Indeed, airfields in these regions have
sometimes had to be closed when low-level clouds (ice fogs) composed
of aircraft-generated ice crystals have proved persistent."
http://atschool.eduweb.co.uk/radgeog/metlink/2001/daily2001/09Feb/0902.html
- quote is found near the bottom of the page.  Website is "MetLink
Report/9 Feb, 2001"

So, yes, contrails can be formed at ground level when the
circumstances are right.

Search - google

Terms - low level contrails, temperature +and contrails, ground level
contrails +in antarctica (note, + signs allow words to be included in
google search)

If I may clarify anything before you rate the answer, please ask.

cheers
digsalot

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Request for Answer Clarification by 911_researcher-ga on 07 Aug 2003 06:37 PDT

Thank you for the excellent and quick response. I have one more
follow-up question: Is it possible for contrails to be formed at low
altitudes at regular, ~60 degree F temperature? I have heard some say
that pressure differentials formed at wing surfaces can create
contrails at any elevation, and I am wondering if this is regardless
of temperature?

I should have specified that with the question, and because this could
be extra work, I will tip you nicely if you can answer it =) If not,
that's okay.

---

Clarification of Answer by digsalot-ga on 07 Aug 2003 14:13 PDT

Hello again.

What you are asking about are wingtip vortices.  They are often
visible when a plane takes off or lands and sometimes even in flight. 
As you say, they are a result of pressure differentials.

Here is a picture of a vortex which has been inhanced by the use of
smoke.
http://www.eng.vt.edu/fluids/msc/gallery/vortex/lh1011.htm - "Gallery
of Fluid Mechanics: Wingtip Vorticies on a commercial aircraft"

"Aircraft in flight, as they create lift, also create wake vortices,"
NASA researcher David Hinton said. "And these can be envisioned as
horizontal tornadoes coming off the wingtips as the aircraft generates
lift, either on approaches or on takeoffs." - quote from "TechTV |
Taming Turbulence"

While these short lived visible lines of condensation are not
contrails in the classic sense of that produced by engine exaust, the
term is often applied to them in a descriptive manner.  This kind of
condensation contrail is also sometimes seen in a storm created
tornado.

So, since the word "contrail" can be applied in all these situations,
then what you have heard is right, a contrail can be formed at any
elevation.

Thank you for your clarification request.  Otherwise I would have
concentrated on the classic exaust created contrail rather than wing
vortices.

I don't look at it as extra work.  It was too interesting a question.

Cheers
digs

Excellent response time, answer, and clarification. Thanks.

IMHO something that looks like a contrail can occur at 68 degrees f =
20 degrees c at low altitude if the humidity is high, perhaps at even
higher temperatures. Ice would not be formed, but fog would, and would
not necessarily appear much different. Recipricating engines that have
heat exchangers on the exhaust manafold can exhaust near ambient
temperature exhaust with high humidity that only needs to cool
slightly to make fog.
 Most types of engines convert fossil fuel to carbon dioxide and water
vapor, so the exhaust does contain several percent water vapor. Jet
and rocket engines are less likely to produce fog at warm ambient
temperatures as the exhaust temperature typically exceeds 1000 degrees
C. Neil